Outstanding account

Good day. I am getting calls and sms's to say that I owe R 800.00 on one of my lines. As explained to the consultant yesterday, I don't agree. I have mailed customer care but have heard nothing back. I have now received another sms! I can not believe that I still owe Cell C a payment.

Payment debited July 4,770.05 Payment made August 5,100.00 – Paid from my FNB account Payment debited September 6,367.00 ???

Total amount paid to Cell C for 3 months is R 16,237.00 ???

Please advise urgently, there is no way that I still owe R 800.00, I paid R 150.00 short on the August payment. Please advise what the R 6,367.00 payments debited on 25,09 & 30/09 is for? I check my accounts each month, I have not as yet had anything that totals R 6,367.00 in one month. I have proof of the above payments made. Thank you.